The present invention relates to the liquid phase dimerization of acrylic compounds to form the corresponding dimers. More specifically, this invention relates to the dimerization of acrylic compounds using a catalyst comprising an organic polymer catalyst support covalently bonded to trivalent pendant atoms, ruthenium complexed with said trivalent pendant atoms, and a second metal selected from the group consisting of Pb and Group VIII metals other than Ru and Pd.
The dimerization of acrylic compounds has long been known. It has also long been known that ruthenium may catalyze the dimerization reaction. U.S. Pat. No. 3,729,498 to Masada, et al discloses the dimerization of acrylonitrile in the presence of a catalyst comprising ruthenium and at least one of bismuth, arsenic, phosphorous and antimony, which may be disposed on a carrier. U.S. Pat. No. 3,790,617, also to Masada, discloses a catalyst for vapor phase dimerization comprising ruthenium salts, which may be deposited on a support, such as active carbon, alumina, silica, silica-alumina, diatomaceous earth and pumice. The '617 patent further discloses that the activity of this catalyst may be enhanced by addition of an alkali metal hydroxide or a mixture of an organo-phosphorous compound combined with a halide of nickel, chromium, molybdenum or tungsten. U.S. Pat. No. 3,981,900 to Chabardes discloses a dimerization process using a catalyst comprising ruthenium which may be used as a solid ruthenium compound, as a finely divided ruthenium compound, in suspension or in solution. This catalyst may be promoted by a Group VIII metal or its oxide or hydroxide. This promoter may be deposited on a support or simply added to the reaction mixture. The promoters Ru(OH).sub.3, RuO(OH).sub.2 and RuO.sub.2 are disclosed as being preferred.
Prior processes had the limitation of using catalysts which show poor conversion or inferior selectivity for the dimer over other undesirable by-products. This results in inefficient use of the acrylic feed and increased cost over a process using a catalyst exhibiting showing good conversion and selectivity for the dimer.
Previous dimerization processes also suffer from several limitations which are minimized or avoided by the process of the present invention. These limitations include homogeneity of the catalyst with the reaction mixture, making separation of the catalyst from the reaction mixture difficult and costly and catalyst recycling impracticable. Due to the fact that a large portion of the operating cost of a process is usually for the catalyst, this made prior processes expensive to perform.
In addition, previous processes used catalysts which, when supported, showed poor leaching characteristics. This resulted in a significant loss of the catalytic compounds to the reaction mixture thereby making recycling impracticable. This was a particularly significant limitation for ruthenium based catalysts due to the relatively high cost of ruthenium metal.